PHYSICS KEYWORDS

Binding energy

The work required to seperate the nucleus into its constituent parts (i.e. protons and neutrons). The greater it is, the more stable the nucleus

Mass defect

The difference between the mass of the nucleus and the total mass of its individual parts

Einstein’s theory of relativity definition

States that mass and energy are related, and mass can be converted to energy and back. This is what happens in nuclear decay, when the products of a decay have lower mass than the original nuclei - the missing mass is converted to energy

Nuclear fusion

2 low-mass nuclei fuse together to create a larger nucleus. In this process the larger nucleus will, therefore, have a greater binding energy per nucleon than the low mass nuclei

Nuclear fission

A large unstable nucleus breaks apart into 2 smaller, more stable nuclei. The binding energgy per nucleon will also increase in this process

Moderator

controls the speed of the neutrons in the thermal nuclear reactor as the speed needs to be a specific value in order to induce fission. Graphite or water can be used and are chosen for their low probability of absorbing neutrons and low mass

Control rods

absorbs neutrons in the thermal nuclear reactor to ensure that there is only one thermal neutron per each fission event. They have the ability to absorb even more neutrons if the rate of release of energy needs to be reduced. The material is chosen on their ability to absorb neutrons effectively.

coolant

extracts the heat in the thermal nuclear reactor and allows it to be transferred to be used to produce electricity. It is usually water or carbon dioxide gas and is used due t the high specific heat capacity of the materials

Shielding in a nuclear reactor

The building housing the reactor is made of concrete walls in order to absorb neutrons and gamma radiation leaving the reactor. The reactor core is also constructed from steel in order to absorb beta radiation as well as some of the gamma radiation and neutrons

Emergency shutdown in a nuclear reactor

Reactors are constructed so that the control rods drop directly into the core to entirely cease fission events if the reactor gets too hot

Remote handling in a nuclear reactor

Fuel rods are operated by these devices

Storage in a nuclear reactor

Strict protocols are in place regarding how to store and transport radioactive waste

Rutherford’s scattering experiment

An ___ in 1908 which provided new evidence about the structure of the atom and resulted in the scientific community moving on from JJ Thomson’s plum pudding model of the atom and adopting Rutherford’s model

Radioactive decay

occurs when an atom is unstable and emits radiation to obtain a more stable state (it is a random process)

Activity

The number of unstabke nuclei that decay per second in a given sample

Half-life (T_1/2)

the amount of time it takes for the activity of the substance to decrease to half its original value

Carbon dating

the examination of the amount of ¹⁴C left in a sample to determine its age as all living organism have a roughly equal ratio to ¹²C to ¹⁴C and when they die, the ¹⁴C slowly decays.

Inverse square law

When the intensity is indirectly proportional to its distance squared

Background radiation

A low level of radiation that is always around on Earth, from both natural and man-made sources of radiation

Natural - nuclear materials in ground, cosmic rays

Man-made - Buildings, nuclear power plants, medical nuclear applications

A nuclear stability graph

A plotting of isotopes by proton number (x-axis) against neutron number (y-axis), classifying them into beta - emitters, alpha emitters, beta + emitters and stable isotopes

Magnetic flux density

force per unit length per unit current on a current-carrying conductor at right-angles to a magnetic field

Fleming’s left hand rule

allows you to determine the direction of motion, field and current in relation to one another

Lenz’s law

the direction of induced current is always such that it is opposed to the change that causes the current

Faraday’s law

the induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit

induced emf

the p.d. induced in a wire due to a moving changing magnetic flux

Cylcotrons

accelerate radioactive particles and control the direction of the particle beams in order to accurately hit the target area on a patient - used in medical machinery to provide radiotherapy treatment

magnetic flux

magnetic field strength through an area

magnetic flux linkage

magnetic field strength through a coil of wire - the flux is multiplied by the number of turns in the coil

Capacitor

an electrical device that stores charge - useful for storing energy and ‘smoothing‘ AC signals in power generation

Capacitance

charge stores per unit p.d.

Dielectrics

any insulating materials which store a charge - tend to be good electrical insulators

Parallel plate capacitor

comprised of 2 parallel conducting plates with a dielectric in between them

relative permittivity (dielectric constant)

ratio of capacitance of the dielectric to the capacitance of the same volume of free space

Time constant (RC)

the time taken for the initial charge, current or voltage to fall to e^-1 (= 0.37) of its initial value, the unit is the second

T_1/2

time taken for half the charge to discharge from the capacitor

Coulomb’s law

gives the electric force between 2 charges

Electric fields

arise due to a charged object and can be represented by field lines that show the path a positive charge would take if placed in the field. It exerts an electrostatic force.

Electric field strength

defined as the force, F, per unit charge, Q, in the field

Electric potential, V

work done per unit charge on a positive charge when it is moved to a given position from infinity. it is zero at infinity

permittivity of free space

the name of a constant ε₀ which = 8.85 × 10^-12 Fm^-1

Force field

A region in which a body experiences a non-contact foce. It can be represented by a vector

Radial field

A field that is spherical and acts towards a central point e,g, gravitational fields

Unifrom field

A field that has no variation e.g. gravitational fields near the surface of planets

Gravitational field strength

th force F per unit mass m on an object in a uniform gravitational field

Gravitational potential energy E_p

The energy possessed by an object due to its place in a gravitational field. This of an object will be zero at infinity as the effects of the gravitational field will be negligible at this distance

Gravitational potential V

The gravitational potential energy per unit mass = work per unit mass to moe an object from infinity to that point. This is zero at infinity

Gravitational potential difference

The difference in gravitational potential between 2 points in space

Equipotential surface

Surfaces of constant potential e.g. orbits

Geostationary satellite

A ____ that has an orbital period around Earth’s equator of one day (24 hours), having a fixed position above the equator. The distance above Earth can be found suing Kepler’s 3rd law. Used in communications and navigation systems e.g. satnav

Synchronous orbit

A specific orbit taken by a satellite where the orbital period is the same as the rotational period and in the same direction of rotation as the object it’s orbitting

Escape velocity

Minimum velocity required for an object to escape the gravitational field of a planet

Specific latent heat of fusion

The ___ for a change from a solid to a liquid, or vice versa

Specific heat of vaporisation

The ___ for a change from a liquid to a gas, or vice versa

Gas laws

A set of experimental laws that look at the relationship between pressure, volume and temperature of a gas

Molar mass

The mass of one mole of substance in kg mol^-1

Molecular mass

The mass of a molecule in u

Absolute zero

-273 ^oC - where the object will have minimum internal energy

Internal energy

the sum of the randomly distributed kinetic energies and potential energies of particles in a system or body

First law of thermodynamic

the change of internal energy of the object is equal to the total energy transfer due to work done and heating

Brownian motion

describes the erratic motion of a small particle when placed on the surface of a fluid. The molecules on the surface of the fluid move randomly on the surface and hit into the particle, making the particle move randomly on the surface - this produces ___, providing evidence for the molecular kinetic energy.

Pressure law

As T is increased in a contained with fixed V, the average speed of molecules increases. This causes molecules to impact the walls of a container with greater force, and p increases. p is directly proportional to T

Charles’ law

As T is increased in a flexible container, the faster moving molecules impact the walls of the container with greater force. If the walls are movable, this increase V while p remains the same. V is directly proportional to T

Boyle’s law

In a case where T is constant, but V is decreased, moleucles have less space to move in between coliisions. This increases the number of collisions, so the total force on the walls of the contained increases, increasing p. p is directly proportional to 1/V

Centripetal force

Causes an object to maintain circular motion - always acts towards the centre of rotation

Simple harmonic motion

Any oscillating motion whose acceleration is proportional to its displacement and opposing in direction to the displacement

Damped Oscillations

____ of systems that will eventually lose their amplitude and energy due to resistance from friction or air resistance

Light damping

Where the time period of an oscillation is independent of the amplitude and, therefore, each wave cycle takes the same amount of time for oscillations to decrease

Critical damping

When the minimum amount of ____ for the system’s oscillation to stop over the course of one oscillation after being released

Heavy damping

____ that is stronger than critical ___ and causes the system to return to equilibrium in a longer amount of time than with critical ___.

Free oscillation

An ____ of a body or system that moves with its natural frequency and is not acted upon by external influence

Forced oscillation

An ___ of a body or system that is initiated by an external influence

Resonance

The situation when the periodic force driving the forced oscillation is in phase with the frequency of the oscillating system

Resonance for light damping

The resonant frequency (frequency at max amplitude) will be the same as the natural frequency. The max amplitude at resonance will be greater

Resonance for heavier damping

The amplitude at resonance reduces. Frequency at which resonance occurs decreases

Kirchoff’s second law

in any electrical circuit, the sum of the electromotive force is equal to the sum of the potential difference in a closed loop

terminal potential difference

the _____ supplied by an electrical power source

electromotive force (emf)

the electrical energy given to charge carriers per unit charge - the p.d. present when there is no current in the source (an ideal cell)

Internal resistance

the ______ of a source that results in energy loss as charge passes through the source, causing a difference between emf and terminal p.d.

Potential divider

the name of a circuit that can be used to alter the p.d. across an output when connected to a fixed input.

A variable potential divider

a ______ with a sliding contact. In this case, the voltage output between 2 of the terminals can be varied by altering the sliding contact

Electric current

the rate of flow of charge through a conductor

net charge

the sum of charges in a body

potential difference

the work done per unit charge

ohm’s law

special case where V is directly proportional to I if temperature and, therefore, resistance are kept constant

conventional current

current from the positive to negative terminal

electric current in metal

the flow of electrons

electric current in electrolyte

the flow of ions

Kirchhoff’s laws - conservation of charge

electric _________ cannot be created or destroyed - total current is constant

Kirchhoff’s first law

the sum of the current into any point in an electrical circuit is equal to the sum of currents out the point

resistivity

a property of a material defined by the product of its resistance and its cross-sectional area divided by its length

Thermistor

An electrical component comprising of a semiconductor with a negative temperature coefficient, meaning that as temperature increases, the resistance of the component will decrease

superconductivity

the phenomenon of resistivity of a material decreasing to zero when the material is cooled at or below the critical temperature. application - production of strong magnetic fields in particle accelerators, reduction of energy loss in transmission of electric power

semiconductors

only conduct electricity over a certain threshold voltage. Below this voltage, the current cannot cross the potential difference gap set up within the diode

Energy

the capacity to do work

Power

the rate of doing work/ the rate of energy transfer

Principle of conservation of energy

For an isolated system, energy is conserved. Energy cannot be created or destroyed, only transferred into different forms.

Hooke’s law

Force applied is directly proportional to the extension of the material unless the elastic limit has been reached

Elastic limit

The point beyond which an object or material cannot return to its original shape and size after the force is removed

Tensile stress

The force per unit cross-sectional area

Tensile strain

The extension per unit length